1. Field of the Invention
The present invention relates to an image display method and apparatus for displaying a special image of a region to be observed obtained by illumination of the region to be observed with special light.
2. Description of the Related Art
Conventionally, endoscope systems for observing tissues in patients' body cavities were widely known. Further, electronic endoscope systems that obtain ordinary images of regions to be observed in patients' body cavities by illuminating the regions with white light, and that display the ordinary images on monitor screens were widely used in practical applications.
As such endoscope systems, for example, a fluorescence endoscope system that obtains an autofluorescence image as well as an ordinary image, and that displays the two images on a monitor screen has been proposed. The fluorescence endoscope system obtains the autofluorescence image by imaging an image of autofluorescence output from the region to be observed by illumination with excitation light.
As the fluorescence endoscope system, a system obtaining a fluorescence image, for example, by injecting ICG (indocyanine green) into a patient's body in advance, and by detecting fluorescence of ICG in patient's blood vessels by illumination of a region to be observed with excitation light has been proposed.
Here, fluorescence images obtained in the aforementioned endoscope systems do not represent an entire region to be observed, such as an organ, but only a light output portion of the region to be observed. Therefore, when the fluorescence image is observed alone, the light output portion of the region to be observed may be observed, but a surrounding region of the light output portion is not observable. Hence, it is impossible to recognize where the light output portion is located in the region to be observed.
To solve such a problem, for example, an ordinary image and a fluorescence image may be displayed at the same time. However, since the two images are displayed separately, it is still impossible to accurately recognize where the light output portion of the fluorescence image is located in the ordinary image.
Therefore, for example, Japanese Unexamined Patent Publication No. 9(1997)-154812 (Patent Document 1), Japanese Unexamined Patent Publication No. 2002-010968 (Patent Document 2), Japanese Unexamined Patent Publication No. 2005-349007 (Patent Document 3), Japanese Unexamined Patent Publication No. 2006-175052 (Patent Document 4), and U.S. Patent Application Publication No. 20070073104 (Patent Document 5) propose recognizing the location of a light output portion of a fluorescence image by generating new synthesis image signals by combining ordinary image signals representing an ordinary image and fluorescence image signals representing a fluorescence image together, and by displaying a synthesis image based on the synthesis image signals.
Further, Japanese Unexamined Patent Publication No. 2008-259591 (Patent Document 6) proposes another method for recognizing the location of a light output portion of a fluorescence image. In Patent Document 6, a light output portion of the fluorescence image and a background image of the light output portion are observed by illuminating a region to be observed with excitation light and by illuminating the region to be observed with illumination light including the wavelength band of fluorescence.
However, when a synthesis image is generated by combining an ordinary image and a fluorescence image together, as in Patent Documents 1 through 5, there is a risk that necessary information becomes unobtainable because it becomes difficult to observe the gradation or the like of the light output portion of the fluorescence image.
Further, when a region to be observed is illuminated with illumination light including the wavelength band of fluorescence, as in Patent Document 6, it is necessary to additionally provide an optical filter, a light source, and the like. Hence, a cost for production increases, and the size of the apparatus becomes large.